Dublin Institute of TechnologyARROW@DIT

Conference Papers Antenna & High Frequency Research Centre

2012-07-08

Vivaldi Array for Generation of UWB CircularPolarizationAdam NarbudowiczDublin Institute of Technology

Matthias JohnDublin Institute of Technology, matthias.john@dit.ie

Xiulong BaoDublin Institute of Technology

Max AmmannDublin Institute of Technology

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Recommended CitationNarbudowicz, A., John, M., Bao, X. L. and Ammann, M. "Vivaldi Array for Generation of UWB Circular Polarization", IEEEInternational Symposium on Antennas and Propagation, Chicago, IL, USA, IEEE Antennas & Propagation Society, Paper 360.2, 08/07/2012.

Vivaldi UWB

Adam NarbudowiAnt

Abstract—A two antenna array is proposedcircular polarization for an ultra-wideband systtwo orthogonal antipodal vivaldi antennas andwhich provides the appropriate phase and amband of interest. The proposed structure is lowmanufacture, offering an axial-ratio bandwidth

I. INTRODUCTION It is only recently that circularly-polarize

can provide good axial ratios (AR) acrbandwidths [1] (with the exception of Furthermore, recent regulations by the FCCCommission triggered a proliferation of awideband (UWB) technology. Such systems ehigh-speed data transmission. It is therefore combine the power efficiency/capacity of advantages of circular polarization.

For classical narrowband systems CP canemploying two orthogonal linearly polarized a90˚ phase shift. In theory the same method cUWB, however practical constraints are morenarrowband systems the 90˚ phase shift is usuaa delay line - a solution which is simple, bRecently UWB phase delay circuits have which employ aperture coupling mechanism good phase stability across very wide bandwdisadvantages of substrate thickness being a dand limited achievable phase shift.

The problem of dual orthogonal linearly antennas has been widely studied [3], [4orthogonal and intersecting antennas are introsuitable for many dual-polarized applicationexhibits certain manufacturing disadvantages and stable phase shift is required across UWBa four rigid horn antenna was successfully emCP, the structure is expensive to manufacturpaper a design involving two linearly poantennas is investigated. The structure consPCBs which are easy to fabricate.

Array for Generation ofB Circular Polarization

cz, Matthias John, Xiulong Bao and Max J. Ammanntenna & High Frequency Research Centre

Dublin Institute of Technology Kevin St., Dublin, Ireland

adam.narbudowicz@mydit.ie

d for generating tem. It consists of d a feed network mplitude over the w cost and easy to

of 74%.

ed (CP) antennas ross very wide spiral antenna).

C and European activity in ultra-enable low-power

advantageous to UWB with the

n be achieved by antennas, fed with can be applied to e demanding. For ally generated by

but band limited. been developed, [2]. These offer

widths, but with design parameter

polarized UWB 4]. Usually two oduced. Although ns, this technique

when a constant B. Although in [5] mployed for UWB re. Hence, in this olarized Vivaldi sists of low-cost

II. DESI

The proposed structure comprisviavaldi antennas, positioned orthospaced by distance D. The general sc

Figure 1. General scheme of t

A. Feed network The feed network consists of a

90˚ phase shifter and a reference lin35, (εr = 3.5 and h = 0.5 mm) and cThree different power dividersconfiguration: a classical T-junctiotransformers, a T-junction with slotstage Wilkinson divider. Both T-junhave poor isolation between the outis different for each output, this camore than 3 dB variation between fantennas and degraded the AR at thoThe use of a Wilkinson divider (wacross the band of interest) overcamsmooth transmission coefficient wantenna feeds. UWB operation wathree stages of the divider [7].

The UWB phase shifter is a employs an aperture coupling technacross UWB is achieved by couplelliptical hole in the ground plane ton the other side of the substrate.applied in the same manner. Thedimensions is shown on Fig. 2Wslot = 7.5 mm, Lslot = 7.2 mm, WeΔW = 2.4 mm, LW1 = 8.4 mm, LW2

f

n

IGN ses a feed network and two ogonally to each other and cheme is shown in Fig. 1.

the proposed antenna.

3dB power divider, UWB ne, printed on Taconic RF-connected as seen in Fig. 1. s were tested for the on with tapered impedance t-line transition [6] and a 3-nction dividers appeared to tput ports. As the next stage aused for some frequencies feeds of the two orthogonal ose frequencies (see Fig. 3). with isolation below 20 dB me this problem, providing ith little variation between as achieved by employing

3 layered structure, which nique [2]. A 45˚ phase shift ling the signal through the to a microstrip line located Then another 45˚ shift is e circuit with all relevant 2. Parameter values are:

Wel = 4.9 mm, Lref = 7.2 mm, = 9 mm and D = 21 mm.

978-1-4673-0462-7/12/$31.00 ©2012 IEEE

Three stages of the divider have characteristi89Ω (terminated by R1 = 107Ω), 71 Ω R2 = 211Ω) and 58Ω (terminated by R3 = 400Ω

Figure 3. Detailed structure of the feed

B. Antenna configuration Two end-fire antipodal vivaldi antennas

using spline curve shapes and an efficient gloalgorithm [8]. Although for linear polarizatiantennas are known for poor cross-polarizatonly necessary that both linearly cross-polarare the same.

Ideally the antennas should be spaced as cin order to keep both phase centers close. Thiswidth of antenna plus spacing needed to prevthe optimization process this was solved by outer point of the spline curve as (14, 100), but relatively narrow vivaldi antenna (40 mm,62 mm on εr = 2.2 in [4]). The optimized described by a spline curve with control point32), (8.7, 49.8), (18, 93.3), (14, 100), (-1, 99),0.8, 30), which is mirrored on the other side oform antipodal vivaldi. A third curve with(5.2, 5), (3.2, 28.7) and (0.8, 30) defines asymmetric 50Ω microstripline to symmetric s

III. RESULTS Simulated results for proposed antenna exh

from 2.6 GHz to 8.3 GHz (plot not shown foshows the simulated boresight AR for configurations. It is seen, that for the independent inputs, a good AR < 3dB is achifrom 3 to 7.5 GHz. This performance degradesjunction is applied due to poor isolation betweA 3-stage Wilkinson divider solves the problem

Fig. 4 shows a two-dimensional plot of the of angle θ and frequency (for convenience 6 dB are grey) for the antenna with 3-stage WThe main lobe with LHCP occurs for θ = 90˚with RHCP can be seen for θ = 270˚. It can beantenna proximity, a small tilt in the main Also the CP beam gets narrower with increasthe electrical distance increases. A comparablefor classical linearly polarized UWB antenna a

ACKNOWLEDGEMENT

ic impedances of (terminated by

Ω).

d network.

s were designed, obal optimization ion the antipodal tion, for CP it is ized components

close as possible, s is limited by the vent coupling. In

y fixing the most resulting in long

, compared to i.e. radiator can be

ts: (0.8, 30), (0.8, , (-0.8, 32) and (-of the substrate to h control points:

a balun from slot.

hibit S11 < -10 dB r brevity). Fig. 3 various antenna feed with two

eved in the band s when simple T-een two channels. m.

AR as a function all values above

Wilkinson divider. ˚ and a back lobe e seen, that due to beam is present. sed frequency, as e problem occurs

arrays [3].

This publication has emanated with the financial support of SciencGrant Number 09/SIRG/I1644.

Figure 3. LHCP gain and axial ra

Figure 4. Axial ratio as a functi

REFERENC

[1] X.L. Bao, and M.J. Ammann, “Printedultra-wide axial-ratio bandwidth,” Propagation, vol. 5, pp. 1089–1096, Ju

[2] A.M. Abbosh, "Ultra-Wideband PMicrowave Theory Tech., 55, (9), pp.

[3] A. Narbudowicz, G. Adamiuk, and WPolarisation Diversity Solution for UltIn Electromagnetic Research Letters, v

[4] G. Adamiuk, T. Zwick, and W. WiesVivaldi antenna for ultra wideband appMicrowave, Radar and Wireless Comm

[5] Z. Hradecky, and P. Hamouz "Researcby Using Quad Ridged Horn AntennAntennas and Propagation, Barcelona

[6] M.E. Bialkowski, and A.M. Abbosh, "of-Phase Power Divider", IEEE MicrLetters, vol. 17, pp. 289-291, April 200

[7] S.B. Cohn, "A Class of Broadband TIEEE Trans. Microwave Theory Tech, v

[8] M. John, and M.J. Ammann, "Computationally Efficient MultiobjeIEEE Trans. Antennas & Propagat, vo

from research conducted ce Foundation Ireland under

atio for boresight (θ = 90O).

ion of angle and frequency.

ES d circularly polarised antenna with IET Microwaves, Antennas &

une 2011. Phase Shifters", IEEE Trans. 1935-1941, 2007. W. Zieniutycz "Clover Array — tra Wideband Systems", Progress

vol. 10, pp. 163-170, August 2009. sbeck "Dual-orthogonal polarized plications", MIKON - Int. Conf. on m., Wroclaw 2008, pp. 1-4. ch of Circular Polarisation Quality na", EuCAP - European Conf. on

2010, pp. 1-5. "Design of a Compact UWB Out-rowave and Wireless Compontnts 07. Three-Port TEM-Mode Hybrids", vol 19, (2), 110-116, 1968. Antenna Optimisation with a ective Evolutionary Algorithm" l. 57, (1), pp. 260-263, 2009.